Tens of thousands of people on Saturday turned out in Germany's largest cities to protest the use of nuclear power in the wake of Japan's Fukushima reactor disaster, police and organizers said.

In Berlin alone more than 100,000 took to the capital's streets to urge Germany's leaders to immediately abolish nuclear power, police spokesman Jens Berger said.

Organizers said some 250,000 people marched at the "Fukushima Warns: Pull the Plug on all Nuclear Power Plants" rallies in the country's four largest cities, making them the biggest anti-nuclear protest in the country's history.

"We can no longer afford bearing the risk of a nuclear catastrophe," Germany's environmental lobby group BUND said.

The disaster at Japan's Fukushima Dai-ichi nuclear facility triggered Chancellor Angela Merkel's conservative government last week to order a temporary shut down of seven of the country's older reactors pending thorough safety investigations. Officials have since hinted several of them might never go back into service.

Protesters shouted "Fukushima, Chernobyl: Too much is too much!" or "Switch them off," urging the government to shut down the country's 17 reactors for good. They also held a minute of silence to remember the victims of Japan's March 11 earthquake and tsunami.

Japanese engineers were frantically attempting on Saturday to pump out puddles of radioactive water at the earthquake-crippled Fukushima nuclear power plant after it injured three workers and delayed efforts to cool reactors to safe levels.

Underscoring growing international qualms about nuclear power raised by the killer earthquake and tsunami in northeast Japan two weeks ago, U.N. Secretary-General Ban Ki-moon said it was time to reassess the international atomic safety regime.

Radioactive water has been found in buildings of three of the six reactors at the power complex 240 km (150 miles) north of Tokyo. On Thursday, three workers sustained burns at reactor No. 3 after being exposed to radiation levels 10,000 times higher than usually found in a reactor.

"Bailing out accumulated water from the turbine housing units before radiation levels rise further is becoming very important," said Japan Nuclear and Industrial Safety Agency senior official Hidehiko Nishiyama.

With no buildings blowing up at Fukushima for a couple of weeks now, global media attention has shifted back to Libya where there is lots of violence to watch. Does this mean that trouble at the 4 wrecked reactors on the East coast of Japan is over?

With the restoration of mains power to the site, there is talk in the media that the situation is now under control. The rate of deterioration has certainly slowed, but there are five slow-burning issues, one working in favor of the authorities and four working against, that will determine the eventual outcome:

1) Radioactive decay of fission products is steadily declining as they burn up, though the rate of decline is slowing as we burn through the short half lives into the intermediate and longer half life inventories of isotopes.

2) Heat accumulation will rise for so long as circulation cooling is absent until a steady state is reached between the reactors and spent fuel and the surrounding buildings.

3) Corrosion of the stainless steel reactor vessel, pipes and pumps in a salt water environment they are not designed to withstand.

Fukushima is like a cancer eating away at the habitat of the east coast of Japan. Whilst the situation appears to be stable, a number of slow burning processes must inevitably be eating away at the heart of these reactors. The solution to a number of these problems is to restore fresh water circulation to each of the cores and the spent fuel ponds. Whether or not the pumping systems work remains to be seen. Disposing of the salty radioactive sludge from inside the reactor vessels presents another major challenge.

It seems possible that the current meta stable condition may persist for many more weeks, and all the while the release and accumulation of radioactive isotopes in the environment will continue. And there is still risk of a catastrophic failure due to heat or corrosion that would result in the status degrading rapidly. It is too early to call this crisis over.

There are now hundreds of radiation-related feeds from Japan on Pachube, monitoring conditions in realtime and underpinning more than half a dozen incredibly valuable applications built by people around the world. They combine 'official' data, 'unofficial' official data, and, most importantly to us, realtime networked geiger counter measurements contributed by concerned citizens. Now we're even seeing some tracking radiation measurements of tap water.

Some of the people to thank for this incredible effort are Shigeru Kobayashi, haiyan zhang, Motoi Shimizu, Takahiro Kakumaru, takashi kondo and Marian Steinbach. Big shout out to all of them!

We've started seeing more and more applications built on top of this incredibly valuable realtime data and so here we are listing all the resources related to this massive crowd-sourced initiative.